<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux-toradex.git/kernel/ptrace.c, branch v3.3-rc5</title>
<subtitle>Linux kernel for Apalis and Colibri modules</subtitle>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/'/>
<entry>
<title>Merge branch 'for-linus' of git://selinuxproject.org/~jmorris/linux-security</title>
<updated>2012-01-15T02:36:33+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2012-01-15T02:36:33+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=c49c41a4134679cecb77362e7f6b59acb6320aa7'/>
<id>c49c41a4134679cecb77362e7f6b59acb6320aa7</id>
<content type='text'>
* 'for-linus' of git://selinuxproject.org/~jmorris/linux-security:
  capabilities: remove __cap_full_set definition
  security: remove the security_netlink_recv hook as it is equivalent to capable()
  ptrace: do not audit capability check when outputing /proc/pid/stat
  capabilities: remove task_ns_* functions
  capabitlies: ns_capable can use the cap helpers rather than lsm call
  capabilities: style only - move capable below ns_capable
  capabilites: introduce new has_ns_capabilities_noaudit
  capabilities: call has_ns_capability from has_capability
  capabilities: remove all _real_ interfaces
  capabilities: introduce security_capable_noaudit
  capabilities: reverse arguments to security_capable
  capabilities: remove the task from capable LSM hook entirely
  selinux: sparse fix: fix several warnings in the security server cod
  selinux: sparse fix: fix warnings in netlink code
  selinux: sparse fix: eliminate warnings for selinuxfs
  selinux: sparse fix: declare selinux_disable() in security.h
  selinux: sparse fix: move selinux_complete_init
  selinux: sparse fix: make selinux_secmark_refcount static
  SELinux: Fix RCU deref check warning in sel_netport_insert()

Manually fix up a semantic mis-merge wrt security_netlink_recv():

 - the interface was removed in commit fd7784615248 ("security: remove
   the security_netlink_recv hook as it is equivalent to capable()")

 - a new user of it appeared in commit a38f7907b926 ("crypto: Add
   userspace configuration API")

causing no automatic merge conflict, but Eric Paris pointed out the
issue.
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
* 'for-linus' of git://selinuxproject.org/~jmorris/linux-security:
  capabilities: remove __cap_full_set definition
  security: remove the security_netlink_recv hook as it is equivalent to capable()
  ptrace: do not audit capability check when outputing /proc/pid/stat
  capabilities: remove task_ns_* functions
  capabitlies: ns_capable can use the cap helpers rather than lsm call
  capabilities: style only - move capable below ns_capable
  capabilites: introduce new has_ns_capabilities_noaudit
  capabilities: call has_ns_capability from has_capability
  capabilities: remove all _real_ interfaces
  capabilities: introduce security_capable_noaudit
  capabilities: reverse arguments to security_capable
  capabilities: remove the task from capable LSM hook entirely
  selinux: sparse fix: fix several warnings in the security server cod
  selinux: sparse fix: fix warnings in netlink code
  selinux: sparse fix: eliminate warnings for selinuxfs
  selinux: sparse fix: declare selinux_disable() in security.h
  selinux: sparse fix: move selinux_complete_init
  selinux: sparse fix: make selinux_secmark_refcount static
  SELinux: Fix RCU deref check warning in sel_netport_insert()

Manually fix up a semantic mis-merge wrt security_netlink_recv():

 - the interface was removed in commit fd7784615248 ("security: remove
   the security_netlink_recv hook as it is equivalent to capable()")

 - a new user of it appeared in commit a38f7907b926 ("crypto: Add
   userspace configuration API")

causing no automatic merge conflict, but Eric Paris pointed out the
issue.
</pre>
</div>
</content>
</entry>
<entry>
<title>ptrace: do not audit capability check when outputing /proc/pid/stat</title>
<updated>2012-01-05T23:53:00+00:00</updated>
<author>
<name>Eric Paris</name>
<email>eparis@redhat.com</email>
</author>
<published>2012-01-03T17:25:15+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=69f594a38967f4540ce7a29b3fd214e68a8330bd'/>
<id>69f594a38967f4540ce7a29b3fd214e68a8330bd</id>
<content type='text'>
Reading /proc/pid/stat of another process checks if one has ptrace permissions
on that process.  If one does have permissions it outputs some data about the
process which might have security and attack implications.  If the current
task does not have ptrace permissions the read still works, but those fields
are filled with inocuous (0) values.  Since this check and a subsequent denial
is not a violation of the security policy we should not audit such denials.

This can be quite useful to removing ptrace broadly across a system without
flooding the logs when ps is run or something which harmlessly walks proc.

Signed-off-by: Eric Paris &lt;eparis@redhat.com&gt;
Acked-by: Serge E. Hallyn &lt;serge.hallyn@canonical.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Reading /proc/pid/stat of another process checks if one has ptrace permissions
on that process.  If one does have permissions it outputs some data about the
process which might have security and attack implications.  If the current
task does not have ptrace permissions the read still works, but those fields
are filled with inocuous (0) values.  Since this check and a subsequent denial
is not a violation of the security policy we should not audit such denials.

This can be quite useful to removing ptrace broadly across a system without
flooding the logs when ps is run or something which harmlessly walks proc.

Signed-off-by: Eric Paris &lt;eparis@redhat.com&gt;
Acked-by: Serge E. Hallyn &lt;serge.hallyn@canonical.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>capabilities: remove task_ns_* functions</title>
<updated>2012-01-05T23:52:59+00:00</updated>
<author>
<name>Eric Paris</name>
<email>eparis@redhat.com</email>
</author>
<published>2012-01-03T17:25:15+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=f1c84dae0ecc51aa35c81f19a0ebcd6c0921ddcb'/>
<id>f1c84dae0ecc51aa35c81f19a0ebcd6c0921ddcb</id>
<content type='text'>
task_ in the front of a function, in the security subsystem anyway, means
to me at least, that we are operating with that task as the subject of the
security decision.  In this case what it means is that we are using current as
the subject but we use the task to get the right namespace.  Who in the world
would ever realize that's what task_ns_capability means just by the name?  This
patch eliminates the task_ns functions entirely and uses the has_ns_capability
function instead.  This means we explicitly open code the ns in question in
the caller.  I think it makes the caller a LOT more clear what is going on.

Signed-off-by: Eric Paris &lt;eparis@redhat.com&gt;
Acked-by: Serge E. Hallyn &lt;serge.hallyn@canonical.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
task_ in the front of a function, in the security subsystem anyway, means
to me at least, that we are operating with that task as the subject of the
security decision.  In this case what it means is that we are using current as
the subject but we use the task to get the right namespace.  Who in the world
would ever realize that's what task_ns_capability means just by the name?  This
patch eliminates the task_ns functions entirely and uses the has_ns_capability
function instead.  This means we explicitly open code the ns in question in
the caller.  I think it makes the caller a LOT more clear what is going on.

Signed-off-by: Eric Paris &lt;eparis@redhat.com&gt;
Acked-by: Serge E. Hallyn &lt;serge.hallyn@canonical.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ptrace: ensure JOBCTL_STOP_SIGMASK is not zero after detach</title>
<updated>2012-01-04T23:01:59+00:00</updated>
<author>
<name>Oleg Nesterov</name>
<email>oleg@redhat.com</email>
</author>
<published>2012-01-04T16:29:20+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=8a88951b5878dc475dcd841cefc767e36397d14e'/>
<id>8a88951b5878dc475dcd841cefc767e36397d14e</id>
<content type='text'>
This is the temporary simple fix for 3.2, we need more changes in this
area.

1. do_signal_stop() assumes that the running untraced thread in the
   stopped thread group is not possible. This was our goal but it is
   not yet achieved: a stopped-but-resumed tracee can clone the running
   thread which can initiate another group-stop.

   Remove WARN_ON_ONCE(!current-&gt;ptrace).

2. A new thread always starts with -&gt;jobctl = 0. If it is auto-attached
   and this group is stopped, __ptrace_unlink() sets JOBCTL_STOP_PENDING
   but JOBCTL_STOP_SIGMASK part is zero, this triggers WANR_ON(!signr)
   in do_jobctl_trap() if another debugger attaches.

   Change __ptrace_unlink() to set the artificial SIGSTOP for report.

   Alternatively we could change ptrace_init_task() to copy signr from
   current, but this means we can copy it for no reason and hide the
   possible similar problems.

Acked-by: Tejun Heo &lt;tj@kernel.org&gt;
Cc: &lt;stable@kernel.org&gt;		[3.1]
Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
This is the temporary simple fix for 3.2, we need more changes in this
area.

1. do_signal_stop() assumes that the running untraced thread in the
   stopped thread group is not possible. This was our goal but it is
   not yet achieved: a stopped-but-resumed tracee can clone the running
   thread which can initiate another group-stop.

   Remove WARN_ON_ONCE(!current-&gt;ptrace).

2. A new thread always starts with -&gt;jobctl = 0. If it is auto-attached
   and this group is stopped, __ptrace_unlink() sets JOBCTL_STOP_PENDING
   but JOBCTL_STOP_SIGMASK part is zero, this triggers WANR_ON(!signr)
   in do_jobctl_trap() if another debugger attaches.

   Change __ptrace_unlink() to set the artificial SIGSTOP for report.

   Alternatively we could change ptrace_init_task() to copy signr from
   current, but this means we can copy it for no reason and hide the
   possible similar problems.

Acked-by: Tejun Heo &lt;tj@kernel.org&gt;
Cc: &lt;stable@kernel.org&gt;		[3.1]
Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>kernel: Map most files to use export.h instead of module.h</title>
<updated>2011-10-31T13:20:12+00:00</updated>
<author>
<name>Paul Gortmaker</name>
<email>paul.gortmaker@windriver.com</email>
</author>
<published>2011-05-23T18:51:41+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=9984de1a5a8a96275fcab818f7419af5a3c86e71'/>
<id>9984de1a5a8a96275fcab818f7419af5a3c86e71</id>
<content type='text'>
The changed files were only including linux/module.h for the
EXPORT_SYMBOL infrastructure, and nothing else.  Revector them
onto the isolated export header for faster compile times.

Nothing to see here but a whole lot of instances of:

  -#include &lt;linux/module.h&gt;
  +#include &lt;linux/export.h&gt;

This commit is only changing the kernel dir; next targets
will probably be mm, fs, the arch dirs, etc.

Signed-off-by: Paul Gortmaker &lt;paul.gortmaker@windriver.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
The changed files were only including linux/module.h for the
EXPORT_SYMBOL infrastructure, and nothing else.  Revector them
onto the isolated export header for faster compile times.

Nothing to see here but a whole lot of instances of:

  -#include &lt;linux/module.h&gt;
  +#include &lt;linux/export.h&gt;

This commit is only changing the kernel dir; next targets
will probably be mm, fs, the arch dirs, etc.

Signed-off-by: Paul Gortmaker &lt;paul.gortmaker@windriver.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ptrace: PTRACE_LISTEN forgets to unlock -&gt;siglock</title>
<updated>2011-09-25T18:02:00+00:00</updated>
<author>
<name>Oleg Nesterov</name>
<email>oleg@redhat.com</email>
</author>
<published>2011-09-25T17:46:22+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=f9d81f61c84aca693bc353dfef4b8c36c2e5e1b5'/>
<id>f9d81f61c84aca693bc353dfef4b8c36c2e5e1b5</id>
<content type='text'>
If PTRACE_LISTEN fails after lock_task_sighand() it doesn't drop -&gt;siglock.

Reported-by: Matt Fleming &lt;matt.fleming@intel.com&gt;
Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
If PTRACE_LISTEN fails after lock_task_sighand() it doesn't drop -&gt;siglock.

Reported-by: Matt Fleming &lt;matt.fleming@intel.com&gt;
Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>connector: add an event for monitoring process tracers</title>
<updated>2011-07-18T19:38:33+00:00</updated>
<author>
<name>Vladimir Zapolskiy</name>
<email>vzapolskiy@gmail.com</email>
</author>
<published>2011-07-15T17:45:18+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=f701e5b73a1a79ea62ffd45d9e2bed4c7d5c1fd2'/>
<id>f701e5b73a1a79ea62ffd45d9e2bed4c7d5c1fd2</id>
<content type='text'>
This change adds a procfs connector event, which is emitted on every
successful process tracer attach or detach.

If some process connects to other one, kernelspace connector reports
process id and thread group id of both these involved processes. On
disconnection null process id is returned.

Such an event allows to create a simple automated userspace mechanism
to be aware about processes connecting to others, therefore predefined
process policies can be applied to them if needed.

Note, a detach signal is emitted only in case, if a tracer process
explicitly executes PTRACE_DETACH request. In other cases like tracee
or tracer exit detach event from proc connector is not reported.

Signed-off-by: Vladimir Zapolskiy &lt;vzapolskiy@gmail.com&gt;
Acked-by: Evgeniy Polyakov &lt;zbr@ioremap.net&gt;
Cc: David S. Miller &lt;davem@davemloft.net&gt;
Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
This change adds a procfs connector event, which is emitted on every
successful process tracer attach or detach.

If some process connects to other one, kernelspace connector reports
process id and thread group id of both these involved processes. On
disconnection null process id is returned.

Such an event allows to create a simple automated userspace mechanism
to be aware about processes connecting to others, therefore predefined
process policies can be applied to them if needed.

Note, a detach signal is emitted only in case, if a tracer process
explicitly executes PTRACE_DETACH request. In other cases like tracee
or tracer exit detach event from proc connector is not reported.

Signed-off-by: Vladimir Zapolskiy &lt;vzapolskiy@gmail.com&gt;
Acked-by: Evgeniy Polyakov &lt;zbr@ioremap.net&gt;
Cc: David S. Miller &lt;davem@davemloft.net&gt;
Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>do not change dead_task-&gt;exit_signal</title>
<updated>2011-06-27T18:30:10+00:00</updated>
<author>
<name>Oleg Nesterov</name>
<email>oleg@redhat.com</email>
</author>
<published>2011-06-22T21:10:11+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=d4f7c511c1c2a67eb287987cf1ce9554149030e6'/>
<id>d4f7c511c1c2a67eb287987cf1ce9554149030e6</id>
<content type='text'>
__ptrace_detach() and do_notify_parent() set task-&gt;exit_signal = -1
to mark the task dead. This is no longer needed, nobody checks
exit_signal to detect the EXIT_DEAD task.

Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Reviewed-by: Tejun Heo &lt;tj@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
__ptrace_detach() and do_notify_parent() set task-&gt;exit_signal = -1
to mark the task dead. This is no longer needed, nobody checks
exit_signal to detect the EXIT_DEAD task.

Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Reviewed-by: Tejun Heo &lt;tj@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>__ptrace_detach: avoid task_detached(), check do_notify_parent()</title>
<updated>2011-06-27T18:30:08+00:00</updated>
<author>
<name>Oleg Nesterov</name>
<email>oleg@redhat.com</email>
</author>
<published>2011-06-22T21:08:53+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=9843a1e977977986d0a4c1000f2229b032572534'/>
<id>9843a1e977977986d0a4c1000f2229b032572534</id>
<content type='text'>
__ptrace_detach() relies on the current obscure behaviour of
do_notify_parent(tsk) which changes tsk-&gt;exit_signal if this child
should be silently reaped. That is why we check task_detached(), it
is true if the task is sub-thread, or it is the group_leader but
its exit_signal was changed by do_notify_parent().

This is confusing, change the code to rely on !thread_group_leader()
or the value returned by do_notify_parent().

Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Acked-by: Tejun Heo &lt;tj@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
__ptrace_detach() relies on the current obscure behaviour of
do_notify_parent(tsk) which changes tsk-&gt;exit_signal if this child
should be silently reaped. That is why we check task_detached(), it
is true if the task is sub-thread, or it is the group_leader but
its exit_signal was changed by do_notify_parent().

This is confusing, change the code to rely on !thread_group_leader()
or the value returned by do_notify_parent().

Signed-off-by: Oleg Nesterov &lt;oleg@redhat.com&gt;
Acked-by: Tejun Heo &lt;tj@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ptrace: implement PTRACE_LISTEN</title>
<updated>2011-06-16T19:41:54+00:00</updated>
<author>
<name>Tejun Heo</name>
<email>tj@kernel.org</email>
</author>
<published>2011-06-14T09:20:18+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=544b2c91a9f14f9565af1972203438b7f49afd48'/>
<id>544b2c91a9f14f9565af1972203438b7f49afd48</id>
<content type='text'>
The previous patch implemented async notification for ptrace but it
only worked while trace is running.  This patch introduces
PTRACE_LISTEN which is suggested by Oleg Nestrov.

It's allowed iff tracee is in STOP trap and puts tracee into
quasi-running state - tracee never really runs but wait(2) and
ptrace(2) consider it to be running.  While ptracer is listening,
tracee is allowed to re-enter STOP to notify an async event.
Listening state is cleared on the first notification.  Ptracer can
also clear it by issuing INTERRUPT - tracee will re-trap into STOP
with listening state cleared.

This allows ptracer to monitor group stop state without running tracee
- use INTERRUPT to put tracee into STOP trap, issue LISTEN and then
wait(2) to wait for the next group stop event.  When it happens,
PTRACE_GETSIGINFO provides information to determine the current state.

Test program follows.

  #define PTRACE_SEIZE		0x4206
  #define PTRACE_INTERRUPT	0x4207
  #define PTRACE_LISTEN		0x4208

  #define PTRACE_SEIZE_DEVEL	0x80000000

  static const struct timespec ts1s = { .tv_sec = 1 };

  int main(int argc, char **argv)
  {
	  pid_t tracee, tracer;
	  int i;

	  tracee = fork();
	  if (!tracee)
		  while (1)
			  pause();

	  tracer = fork();
	  if (!tracer) {
		  siginfo_t si;

		  ptrace(PTRACE_SEIZE, tracee, NULL,
			 (void *)(unsigned long)PTRACE_SEIZE_DEVEL);
		  ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL);
	  repeat:
		  waitid(P_PID, tracee, NULL, WSTOPPED);

		  ptrace(PTRACE_GETSIGINFO, tracee, NULL, &amp;si);
		  if (!si.si_code) {
			  printf("tracer: SIG %d\n", si.si_signo);
			  ptrace(PTRACE_CONT, tracee, NULL,
				 (void *)(unsigned long)si.si_signo);
			  goto repeat;
		  }
		  printf("tracer: stopped=%d signo=%d\n",
			 si.si_signo != SIGTRAP, si.si_signo);
		  if (si.si_signo != SIGTRAP)
			  ptrace(PTRACE_LISTEN, tracee, NULL, NULL);
		  else
			  ptrace(PTRACE_CONT, tracee, NULL, NULL);
		  goto repeat;
	  }

	  for (i = 0; i &lt; 3; i++) {
		  nanosleep(&amp;ts1s, NULL);
		  printf("mother: SIGSTOP\n");
		  kill(tracee, SIGSTOP);
		  nanosleep(&amp;ts1s, NULL);
		  printf("mother: SIGCONT\n");
		  kill(tracee, SIGCONT);
	  }
	  nanosleep(&amp;ts1s, NULL);

	  kill(tracer, SIGKILL);
	  kill(tracee, SIGKILL);
	  return 0;
  }

This is identical to the program to test TRAP_NOTIFY except that
tracee is PTRACE_LISTEN'd instead of PTRACE_CONT'd when group stopped.
This allows ptracer to monitor when group stop ends without running
tracee.

  # ./test-listen
  tracer: stopped=0 signo=5
  mother: SIGSTOP
  tracer: SIG 19
  tracer: stopped=1 signo=19
  mother: SIGCONT
  tracer: stopped=0 signo=5
  tracer: SIG 18
  mother: SIGSTOP
  tracer: SIG 19
  tracer: stopped=1 signo=19
  mother: SIGCONT
  tracer: stopped=0 signo=5
  tracer: SIG 18
  mother: SIGSTOP
  tracer: SIG 19
  tracer: stopped=1 signo=19
  mother: SIGCONT
  tracer: stopped=0 signo=5
  tracer: SIG 18

-v2: Moved JOBCTL_LISTENING check in wait_task_stopped() into
     task_stopped_code() as suggested by Oleg.

Signed-off-by: Tejun Heo &lt;tj@kernel.org&gt;
Cc: Oleg Nesterov &lt;oleg@redhat.com&gt;
</content>
<content type='xhtml'>
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<pre>
The previous patch implemented async notification for ptrace but it
only worked while trace is running.  This patch introduces
PTRACE_LISTEN which is suggested by Oleg Nestrov.

It's allowed iff tracee is in STOP trap and puts tracee into
quasi-running state - tracee never really runs but wait(2) and
ptrace(2) consider it to be running.  While ptracer is listening,
tracee is allowed to re-enter STOP to notify an async event.
Listening state is cleared on the first notification.  Ptracer can
also clear it by issuing INTERRUPT - tracee will re-trap into STOP
with listening state cleared.

This allows ptracer to monitor group stop state without running tracee
- use INTERRUPT to put tracee into STOP trap, issue LISTEN and then
wait(2) to wait for the next group stop event.  When it happens,
PTRACE_GETSIGINFO provides information to determine the current state.

Test program follows.

  #define PTRACE_SEIZE		0x4206
  #define PTRACE_INTERRUPT	0x4207
  #define PTRACE_LISTEN		0x4208

  #define PTRACE_SEIZE_DEVEL	0x80000000

  static const struct timespec ts1s = { .tv_sec = 1 };

  int main(int argc, char **argv)
  {
	  pid_t tracee, tracer;
	  int i;

	  tracee = fork();
	  if (!tracee)
		  while (1)
			  pause();

	  tracer = fork();
	  if (!tracer) {
		  siginfo_t si;

		  ptrace(PTRACE_SEIZE, tracee, NULL,
			 (void *)(unsigned long)PTRACE_SEIZE_DEVEL);
		  ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL);
	  repeat:
		  waitid(P_PID, tracee, NULL, WSTOPPED);

		  ptrace(PTRACE_GETSIGINFO, tracee, NULL, &amp;si);
		  if (!si.si_code) {
			  printf("tracer: SIG %d\n", si.si_signo);
			  ptrace(PTRACE_CONT, tracee, NULL,
				 (void *)(unsigned long)si.si_signo);
			  goto repeat;
		  }
		  printf("tracer: stopped=%d signo=%d\n",
			 si.si_signo != SIGTRAP, si.si_signo);
		  if (si.si_signo != SIGTRAP)
			  ptrace(PTRACE_LISTEN, tracee, NULL, NULL);
		  else
			  ptrace(PTRACE_CONT, tracee, NULL, NULL);
		  goto repeat;
	  }

	  for (i = 0; i &lt; 3; i++) {
		  nanosleep(&amp;ts1s, NULL);
		  printf("mother: SIGSTOP\n");
		  kill(tracee, SIGSTOP);
		  nanosleep(&amp;ts1s, NULL);
		  printf("mother: SIGCONT\n");
		  kill(tracee, SIGCONT);
	  }
	  nanosleep(&amp;ts1s, NULL);

	  kill(tracer, SIGKILL);
	  kill(tracee, SIGKILL);
	  return 0;
  }

This is identical to the program to test TRAP_NOTIFY except that
tracee is PTRACE_LISTEN'd instead of PTRACE_CONT'd when group stopped.
This allows ptracer to monitor when group stop ends without running
tracee.

  # ./test-listen
  tracer: stopped=0 signo=5
  mother: SIGSTOP
  tracer: SIG 19
  tracer: stopped=1 signo=19
  mother: SIGCONT
  tracer: stopped=0 signo=5
  tracer: SIG 18
  mother: SIGSTOP
  tracer: SIG 19
  tracer: stopped=1 signo=19
  mother: SIGCONT
  tracer: stopped=0 signo=5
  tracer: SIG 18
  mother: SIGSTOP
  tracer: SIG 19
  tracer: stopped=1 signo=19
  mother: SIGCONT
  tracer: stopped=0 signo=5
  tracer: SIG 18

-v2: Moved JOBCTL_LISTENING check in wait_task_stopped() into
     task_stopped_code() as suggested by Oleg.

Signed-off-by: Tejun Heo &lt;tj@kernel.org&gt;
Cc: Oleg Nesterov &lt;oleg@redhat.com&gt;
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